space profiling

In my mail, the reason for the `save flags some where' and `restore flags
from some where' was the idea that the entire rest of the code generator
could be completely unaware that any thing was going on. If this is no big
deal to the code generator, then it looks like the 2 parallel arrays is the
way to go.
As to the 64 bit integer support, for now just using IntInf's should be fine.
It isn't like mlprof does much. As to the code in the program being
profiled, I would still probably vote (weakly) for doing this in C. With the
global nature of MLton, any ML code could cause changes in other things.